mm: page_alloc: revert inadvertent !__GFP_FS retry behavior change

Historically, !__GFP_FS allocations were not allowed to invoke the OOM
killer once reclaim had failed, but nevertheless kept looping in the
allocator.

Commit 9879de7 ("mm: page_alloc: embed OOM killing naturally into
allocation slowpath"), which should have been a simple cleanup patch,
accidentally changed the behavior to aborting the allocation at that
point.  This creates problems with filesystem callers (?) that currently
rely on the allocator waiting for other tasks to intervene.

Revert the behavior as it shouldn't have been changed as part of a
cleanup patch.

Fixes: 9879de7 ("mm: page_alloc: embed OOM killing naturally into allocation slowpath")
Signed-off-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reported-by: Tetsuo Handa <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Cc: Dave Chinner <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: <[email protected]>	[3.19.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/page_alloc.c

@@ -2353,8 +2353,15 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
 		if (ac->high_zoneidx < ZONE_NORMAL)
 			goto out;
 		/* The OOM killer does not compensate for light reclaim */
-		if (!(gfp_mask & __GFP_FS))
+		if (!(gfp_mask & __GFP_FS)) {
+			/*
+			 * XXX: Page reclaim didn't yield anything,
+			 * and the OOM killer can't be invoked, but
+			 * keep looping as per should_alloc_retry().
+			 */
+			*did_some_progress = 1;
 			goto out;
+		}
 		/*
 		 * GFP_THISNODE contains __GFP_NORETRY and we never hit this.
 		 * Sanity check for bare calls of __GFP_THISNODE, not real OOM.